The present invention relates to a solid-state imaging device used for a color television camera, and more particularly to a MOS solid-state imaging device which scans two-dimensionally arranged pixels by an X-Y switch matrix.
In solid-state imaging devices, a number of two-dimensionally arranged pixels each having a function of storing a signal charge representing a sensed light and scan means for reading the signal charges from the pixels in a predetermined sequence are integrally solidified by semiconductor integration circuit technology. Of those solid-state imaging devices, one which scans by the X-Y matrix is called an X-Y address type (or MOS type), and various drive methods therefor have been proposed. For example, in a solid-state imaging device shown in JP-A-59-144278 by the present assignee, particularly in FIG. 5, two lines of pixels are parallelly and horizontally scanned, where the horizontal direction (X-direction) of the pixel array is defined as a row and the vertical direction (Y-direction) is defined as a column. For an interlaced scan, a combination of two rows of pixels which are parallelly scanned is changed between an odd-numbered field and an even-numbered field by an interlace switch so that signal charges are read from all pixels in each field. As a result. no residual image is produced.
In color imaging, a plurality of chrominance signals must be parallelly produced, and the two-row parallel scan system described above is suitable for the purpose. Color imaging by the two-row parallel scan system is explained below.
For color imaging, color filters are provided one for each pixel. FIG. 1 shows an example of arrangement of the color filters. W denotes a transparent filter, G denotes a green light transmission filter, Cy denotes a cyan light transmission filter, and Ye denotes a yellow light transmission filter. They are referred to as W, G, Cy and Ye filters, respectively. Two rows, n-th and (n+1)th rows are shown in FIG. 1 and filters for four pixels in each row are shown. In the n-th row, the W filters are arranged at every other pixel and the G filters are arranged at another set of every other pixel. In the (n+1)th row, the Cy filters are arranged at every other pixel and the Ye filters are arranged at another set of every other pixel.
In the solid-state imaging device shown in the above JP-A-59-144278, two rows of pixels are parallelly scanned. When the filter array shown in FIG. 1 is applied to that solid-state imaging device and the n-th and (n+1)th rows are parallelly scanned, a first signal is produced from the n-th row, which signal alternately comprises signal charges (W charges) from the pixels covered by the W filters and G charges, and a second signal is produced from the (n+1)th row, which signal alternately comprises Cy charges and Ye charges. The first and second signals are two-phase sampled. The first signal is separated into the W charges and the G charges to produce a signal (W signal) which comprises the W charges and a G signal which comprises the G charges. Similarly, the second signal is separated into the Cy charges and Ye charges to produce a Cy signal and a Ye signal. An r (red) signal and a b (blue) signal are synthesized from those signals as follows. EQU r=(W-Cy)+(Ye-G) (1) EQU b=(W-Ye)+(Cy-G) (2)
An intensity signal Y is produced by adding the first and second signals.
The above technique provides one method of color imaging but includes the following problems because it separates the signals by the two-phase sampling.
(1) A configuration of a sampling circuit and a sampling pulse generator for driving the sampling circuit is complex.
(2) The signal produced by the sampling includes noises at a sampling frequency and frequencies of high-order harmonics and hence an S/N ratio of the signal is low.
The item (2) creates a problem when a signal which includes noises having a spectrum which increases with the frequency such as a signal produced by amplifying an output signal of the solid-state imaging device by a feedback preamplifier is applied to the sampling circuit.
Accordingly, it is desirable to produce separate signals for the respective pixels having different color filters, without sampling.
One approach thereto is to arrange two horizontal signal lines for each row so that the signal charges from the pixels having the same color filters are transferred to one of the signal lines. Thus, the signal charges read through different color filters are transferred to the other signal line and hence the sampling is not necessary. However, this approach increases the wiring space necessary for the horizontal signal lines and decreases the space factor (aperture factor) of the pixels, resulting in reduction of sensitivity.